This invention relates to a servo steering system for automotive vehicles within which a vehicle speed dependent reaction sensing force is developed to resist manual steering effort applied.
Such speed dependent fluid powered steering systems wherein the degree of fluid reaction force developed is varied as a function of vehicle speed, is already known, as disclosed, for example, in the FIG. 10 embodiment of German Pat. OS No. 2707 991. In the foregoing prior art disclosure, a control device is shifted by a regulator to vary the flow rate of pressurized fluid from a pump and the supply of regulated reaction pressure fluid to reaction chambers. In such arrangement, two reaction chambers are interconnected and thereby subject to the same fluid reaction pressure. The valve pistons associated with a steering control valve assembly act as reaction pistons subject to the reaction pressure and are therefore limited in movement by valve housing stops permitting movement of only one piston for each steering direction. The valve pistons are not therefore restrictively controlled during operational movements so that unintended steering motion may automatically occur as a result of manlfunction. In the event there is a failure in the generation of regulated reaction pressure, the control valve assembly operates without reaction so that the steering operation will not provide any steering sense to the driver and unintended steering forces may be developed. According to other prior art arrangements, pressurized fluid from a servo pump is supplied through flow restrictors to opposing reaction chambers. The reaction chambers are hydraulically separated from each other either by the control valve and/or by one-way check valves. Such prior art arrangements produce a discontinuous reaction force during travel of the control valve through the neutral position and damping of forces because of abrupt closing of the check valves.
It is therefore an important object of the present invention to provide a low cost servo steering system in which a vehicle speed dependent reaction force is developed without the disadvantages of the aforementioned prior art arrangements.